KR101367064B1 - Process for recycling product streams separated from a hydrocarbon-containing feed stream - Google Patents

Abstract

The present invention provides a process for recycling a product stream separated from a hydrocarbon containing feed stream comprising olefin monomers, olefin comonomers, hydrocarbon diluents and components such as H ₂ , N ₂ , O ₂ , CO, CO ₂ and formaldehyde. It is about. According to the process, the hydrocarbon-containing feed stream is a) a first side stream comprising a hydrocarbon diluent and an olefin monomer, b) a second side stream substantially free of hydrogen and comprising a hydrocarbon diluent and an olefin monomer, c) substantially Bottom stream comprising an olefin free hydrocarbon diluent and d) olefin monomers, hydrocarbon diluents and formaldehyde, H ₂ , N ₂ , O ₂ , CO and CO ₂ Separated into components such as The process also includes recycling the first and second side streams in a polymerization process to prepare a bimodal polyolefin.

Description

Process for recycling product stream separated from hydrocarbon containing feed stream {PROCESS FOR RECYCLING PRODUCT STREAMS SEPARATED FROM A HYDROCARBON-CONTAINING FEED STREAM}

The present invention relates generally to olefin polymerization. In particular, the present invention relates to a process for separating a hydrocarbon-containing feed stream comprising an olefin monomer, at least one optional co-monomer and a hydrocarbon diluent into another product stream and for preparing a bimodal polyolefin. Recycling of the product stream separated in the polymerization process. The present invention therefore relates to the optimization of the recycling system and process during olefin polymerization.

Olefin polymerization is often carried out in the reactor with monomers, diluents and catalysts and optionally comonomers and hydrogen. When the polymerization is carried out under slurry conditions, the product usually consists of solid particles and is in suspension in the diluent. The slurry contents of the reactor are continuously circulated to the pump to maintain an efficient suspension of polymer solid particles in the liquid diluent. The product is discharged by a settling leg that operates on a batch principle to recover the product. Sedimentation in the legs is used to increase the solids concentration of the slurry finally recovered as product slurry.

Alternatively, the product slurry can be fed to a second reactor connected in series to the first reactor from which the second polymer fraction can be produced. Typically, when two reactors are used in series in this manner, the resulting polymer product comprises a bimodal polymer product comprising a first polymer fraction produced in a first reactor and a second polymer fraction produced in a second reactor. And have a bimodal molecular weight distribution. The resulting product will also usually consist of solid particles in suspension in a diluent and then exit the second reactor using the settling legs in a similar manner as described above.

The product slurry recovered in the olefin polymerization process comprises a slurry of polymer solids in a liquid containing diluent, dissolved unreacted monomer and optionally dissolved unreacted comonomer. Typically, this liquid also comprises traces of heavier urea, such as oligomers, and lighter components, including H ₂ , N ₂ , O ₂ , CO and / or CO ₂ . The catalyst will generally be included in the polymer.

Once recovered from the reactor, the product slurry is discharged to a flash tank via a flash line where most of the diluent and unreacted monomers and optionally unreacted comonomer are flashed off. Thereafter, it is highly desirable to further treat the steam to recover unreacted monomers, optionally unreacted comonomers and diluents, because it is necessary to reuse these separate components comprising monomers, comonomers and diluents in the polymerization process. Is economically beneficial.

In the art, it is known that vapor streams comprising unreacted monomers, unreacted comonomers and diluents effluent from the effluent of the polymerization process can be treated in a distillation system to separate the components. Traditionally, diluents are collected through a complex process so that such diluents can be recycled to the reactor.

US Pat. No. 4,589,957 describes, for example, a process for separating hydrocarbon-containing vapor streams comprising monomers, comonomers and diluents which have been discharged from the effluent of the monopolymerization and / or copolymerization process. The process described includes a vapor stream undergoing two stage distillation with a common accumulation zone, from which the condensate is used as a source for the second distillation and as a reflux source for the first distillation. Play a role.

However, a problem encountered in many distillation systems is the sub-optimal separation of lighter components including H ₂ , N ₂ , O ₂ , CO and / or CO ₂ recovered from the diluent. As a result, the use of separate diluent streams containing these components in the polymerization process may seriously reduce the polymerization efficiency resulting in suboptimal polymerization conditions. In particular, when reusing a separate diluent stream in a polymerization process to prepare a bimodal polymer product, for example, recovery of the diluent stream is required and the residual amount of lighter components, such as hydrogen, so that the diluent stream can be used in the reactor. This substantially reduced and higher molecular weight component of the bimodal polymer product is prepared.

An example of a recovery process that is currently applied to meet this requirement involves the creation of a large amount of diluent stream that is substantially free of olefins. However, this recovery process involves the reuse of diluent streams which are in fact too pure for this use and are too expensive to use due to the substantial lack of olefin monomers. Moreover, suitable separation methods for recovering large amounts of diluent substantially free of olefins involve a number of problems and drawbacks, among others, requiring large amounts of energy to perform the separation process; Increasing the amount of olefin monomer that must be separated from the lighter component as described above; Increasing the loss of olefin monomers and reducing the stability of the distillation system.

For this reason, in the art, in particular, for the optimized process for recycling a hydrocarbon-containing feed stream which needs to be separated into a stream which can be recycled to the polymerization process, for example a bimodal polyolefin such as bimodal polyethylene is prepared. There are many demands. There is also a need in the art to provide a diluent recycle process that is less costly to configure and / or operate.

Applicant provides a process that overcomes at least some of the problems described above. There is provided an optimized process for separating the hydrocarbon containing feed stream into other product streams and reusing the separated product stream. In particular, the process provided herein can optimally recycle the separated stream in a polymerization process to prepare a bimodal polymer.

In a first aspect, the invention provides an olefin monomer, at least one optional olefin comonomer, a hydrocarbon diluent and H ₂ , N ₂ , O ₂ , CO, CO ₂ And a process for recycling a product stream separated from a hydrocarbon containing feed stream comprising components such as and formaldehyde, the hydrocarbon containing feed stream comprising:

a) the feed stream is

   a1) a bottoms stream comprising a hydrocarbon diluent and at least one optional comonomer, and

a2) hydrocarbon diluent, olefin monomer and H ₂ , N ₂ , O ₂ , CO, CO ₂ An overhead stream containing components such as and formaldehyde

Introducing the feed stream into a first distillation column to undergo distillation conditions suitable to remove the;

b) storing the condensate in a separator 108 suitable for condensing the overhead stream exiting the first distillation column in step a2) to form a condensate and separating the vapor stream and the liquid stream;

c) olefin monomers, hydrocarbon diluents and formaldehyde, H ₂ , N ₂ , O ₂ , CO and CO ₂ Removing the vapor stream from the separator comprising a component such as;

d) storing the condensate in a separator suitable for condensing the vapor stream removed in step c) to form a condensate and separating the vapor stream and the liquid stream 15;

e) removing the liquid stream of step d) from the separator;

f) separating the liquid stream into a first side stream comprising a hydrocarbon diluent and an olefin monomer and the remaining stream;

g) introducing the remaining stream into a second distillation column and the remaining stream

   g1) a bottoms stream comprising a hydrocarbon diluent substantially free of olefins,

   g2) a substantially hydrogen free second side stream comprising a hydrocarbon diluent and an olefin monomer, and

g3) overhead vapor stream comprising olefin monomers, hydrocarbon diluents and components such as formaldehyde, H ₂ , N ₂ , O ₂ , CO and CO ₂

Separated by subjecting to suitable distillation conditions to remove them.

According to the method, it is also known that the vapor stream exiting the separator of the first distillation column is sent / supplied to the overhead condenser of the second distillation column. Thus, the invention is characterized in that it comprises at least two condensation / separation cycles provided in series. This advantageously limits monomer losses, thus lowering production costs. In particular, when producing polyethylene, this mode of operation allows ethylene purge to limit ethylene loss in the case of a reactor in a bimodal configuration. In another embodiment of this process, a portion of the condensate stored in step b) is removed as a liquid stream and passed as reflux to the first distillation column.

In a preferred embodiment, the invention is recycled in a polymerization process for preparing a bimodal polyolefin comprising at least two different polyolefin fractions obtained in two different polymerization reactors in which the first and second side streams are connected to each other in series. One of the fractions has a higher molecular weight than the other fraction, the second side stream is reused in a polymerization process in which a polyolefin fraction having a higher molecular weight is prepared, and the first side stream is recycled to the other polyolefin fraction. It provides a process to be reused in this prepared polymerization process.

In other words, the process includes recycling the first and second side streams in a polymerization process to prepare a bimodal polyolefin comprising at least two different polyolefin fractions obtained in two different polymerization reactors connected in series with each other. Wherein one of the fractions has a higher molecular weight than the other one. The second side stream is reused in the polymerization process in which the higher molecular weight polyolefin fraction is prepared, and the first side stream is reused in the polymerization process in which the other polyolefin fraction, ie, the lower molecular weight polyolefin fraction, is prepared. Thus, the first side stream can be fed to the reactor in which the polyolefin fraction having a higher molecular weight is prepared, and the second side stream can be fed to the reactor in which the other polyolefin fraction is prepared.

In another embodiment, the invention is a process wherein the bottom stream of step g1) is reused in a polymerization process for preparing a bimodal polyolefin comprising at least two different polyolefin fractions obtained in two different polymerization reactors connected in series with each other. Wherein one of the fractions has a higher molecular weight than the other fraction and the bottom stream is reused in a polymerization process in which a polyolefin fraction having a higher molecular weight is prepared.

In another embodiment, the present invention condenses the overhead vapor stream obtained in step g3) in a mixture of the vapor stream removed in step c) to optionally form a condensate and so formed in the separator. Storing the step; i) subjecting the stored condensate obtained in step h) to steps e) to g).

Preferably, this process is carried out with the olefin monomer and formaldehyde, H ₂ , N ₂ , O ₂ , CO and CO ₂ from the condensate stored in step d). Removing the vapor stream comprising components such as, and recovering the olefin monomer from the vapor stream.

In another embodiment, the present invention is directed to removing 1) a side stream comprising at least one optional comonomer, 2) an overhead stream comprising a hydrocarbon diluent and optionally a comonomer, and 3) a bottom stream comprising heavy components. A process which may further comprise the step of introducing a bottoms stream of step a1) into a third distillation column (3) such that the bottoms stream is subjected to suitable distillation conditions.

Preferably, the side stream 1), when counted from the bottom of the tower, is carried at the bottom of the distillation column, for example in the tray 3 of the tower. In general, the overhead stream of the third distillation column will contain only a small amount of comonomer.

This overhead stream of the third distillation column containing the hydrocarbon diluent can be fed back to the first distillation column. Preferably, the overhead stream from the top of the third distillation column is first cooled in an overhead condenser of the third distillation column. The condensed stream exiting the outlet of the condenser of the third distillation column is then collected in the reflux drum of the third distillation column. The condensate can then be divided into two parts: the first part of which is sent to the third distillation column as reflux and the second part is recycled to the first distillation column as feed.

Alternatively or in combination, the bottom stream of step a1) may also advantageously be reused in the polymerization process for preparing the bimodal polyolefin. In particular, it can be fed to a reactor in which a polyolefin fraction having a higher molecular weight fraction is prepared. In the bimodal configuration, the reactor in which the polyolefin fraction with higher molecular weight fraction is prepared is also the reactor with the highest comonomer (eg hexene) concentration.

It should be noted that all values given herein in ppm are intended to refer to weight ppm values. Therefore, the terms "ppm" and "weight ppm" are used synonymously herein.

In another embodiment, the present invention provides a process wherein said first side stream of step f) comprises at least 3 wt%, more preferably at least 5 wt% olefin monomer. In another embodiment, the present invention provides a process wherein said first side stream of step f) comprises less than 10 wt% olefin monomer, eg, less than 8 wt% olefin monomer.

In another embodiment, the present invention provides a process wherein said first side stream of step f) comprises 100-10000 ppm by weight of hydrogen, preferably 100-5000 ppm by weight of hydrogen. In a preferred embodiment, the first side stream of step f) comprises less than 500 ppm by weight of hydrogen.

In another embodiment, the present invention provides a process wherein said second side stream of step g2) is removed from the upper third of said second distillation column. In an embodiment, the present invention provides a process wherein said second side stream of step g2) comprises at least 2 wt% olefin monomer, preferably at least 2.5 wt%, and more preferably at least 3 wt% olefin monomer. In another embodiment, the present invention provides a process wherein the second side stream of step g2) comprises at most 5 ppm by weight, preferably at most 2 ppm by weight, more preferably at most 1 ppm by weight of hydrogen.

In another embodiment, the present invention provides a process wherein said bottom stream of step g1) comprises less than 5 ppm by weight of olefin monomer, preferably less than 1 ppm by weight of olefin monomer. In another embodiment, the present invention provides a process wherein said bottom stream of step g1) comprises less than 5000 ppm by weight of olefin comonomer.

In another preferred embodiment, a process is provided wherein said hydrocarbon-containing feed stream comprising olefin monomers, comonomers and hydrocarbon diluents is an effluent stream obtained from a polymerization process for preparing a monomodal or bimodal polyolefin. Preferably, the olefin monomer is ethylene, the comonomer is 1-hexene and the hydrocarbon diluent is isobutane.

The process involves recovery of the side stream that is substantially free of hydrogen. This side stream is as rich as possible of the olefin monomer and still low enough of hydrogen so that it can be fed to the reactor where a higher molecular weight polymer fraction is prepared during the bimodal polymerization process. As a result, the need to use olefin free hydrocarbon streams for the same purpose is greatly reduced. Since the flow rate of steam used for reboiling of the distillation column is directly proportional to the flow rate of the olefin-free hydrocarbon stream to be obtained as the bottom stream, reducing this bottom stream reduces the steam consumption required to ensure proper reboiling of the column. Considerably more.

Another advantage of the present invention is that the substantially hydrogen-free side stream absorbs the olefin monomer and thus contains most of the hydrogen entering the recycle compartment and can be condensed to be removed from the recycle compartment and sent to the monomer recovery unit. The vapour stream will be reduced considerably, eg by at least 50%. Therefore, the present invention makes it possible to recover more of the olefin monomer introduced into the recycle compartment before being sent to the recovery unit as compared to the currently applied recovery process. For example, the present invention makes it possible to recover more of the ethylene monomer introduced into the recycle compartment before being sent to the ethylene recovery unit (ERU) compared to the currently applied recovery process. According to the process, the recovery of the substantially hydrogen free side stream from the hydrocarbon feed stream allows to considerably reduce the loss of ethylene monomer.

In addition, according to the process, less condensable vapor streams containing lighter components need to be sent to the monomer recovery unit, and the size of the monomer recovery unit, for example, the ethylene recovery unit, can be significantly reduced. This has important economic and environmental impacts and advantages.

In addition, unexpectedly, Applicants have: a) a first side stream comprising a hydrocarbon diluent and an olefin monomer, b) a second side stream substantially free of hydrogen and a hydrocarbon diluent and an olefin monomer, c) substantially free of olefins. Bottom stream comprising a hydrocarbon diluent and d) the remaining olefin monomer, the remaining hydrocarbon diluent and formaldehyde, H ₂ , N ₂ , O ₂ , CO and CO ₂ It has been found that this process involving the recovery of an overhead vapor stream comprising the remaining components, such as, has improved efficiency and stability when compared to conventional distillation systems that lack recovery of the second side stream.

This optimized recovery process is particularly suitable for providing a diluent stream for reuse in a polymerization system for preparing bimodal polymer products. In particular, the invention can be used in a reactor in which a substantially hydrogen-free diluent side stream can be used in a reactor in which a higher molecular weight fraction of a bimodal polymer is prepared, and a reactor in which a lower molecular weight fraction of a bimodal polymer is prepared. Process to separate and recover the diluent side stream. Thus, the process optimally provides two side streams that can each be reused to feed the diluent to each reactor that is subjected to a polymerization process for preparing bimodal polyolefins, for example bimodal polyethylene.

In another aspect, the present invention also provides

Feeding an olefin monomer, diluent, at least one polymerization catalyst, optionally hydrogen and one or more optional olefin comonomer (s) to the first reactor,

Polymerizing the olefin monomer in the first reactor to produce a polymer slurry comprising a first polyolefin fraction in a diluent,

Moving said polymer slurry from said first reactor to a second reactor,

Feeding an olefin monomer, diluent, optionally hydrogen and one or more optional olefin comonomer (s) to the second reactor,

Polymerizing the olefin monomer and the at least one optional olefin comonomer (s) in the second reactor to produce a slurry in a diluent comprising a second polyolefin fraction having a molecular weight different from the polyolefin fraction produced in the first reactor. step,

Evacuating from the second reactor a slurry comprising bimodal polyolefin in the diluent,

Recovering the bimodal polyolefin from the slurry by separating at least most of the diluent from the slurry in a hydrocarbon containing feed stream, and

At least two different polyolefin fractions obtained in two different polymerization reactors in series, comprising the step of allowing said hydrocarbonaceous feed stream to go through a process as described above, one of said fractions having a higher molecular weight Eggplant relates to the use of the process according to the invention in a polymerization process for preparing bimodal polyolefins, such as for example bimodal polyolefins.

In another aspect, the invention is also a polymerization system for preparing a bimodal polyolefin comprising two polymerization reactors operably interconnected in series to a distillation system, the distillation system being operably interconnected in series. A distillation column and a second distillation column,

A hydrocarbon containing feed stream comprising an olefin monomer, optionally one or more comonomers and a hydrocarbon diluent,

  A bottoms stream comprising a hydrocarbon diluent and at least one optional comonomer, and

Hydrocarbon diluents, olefin monomers and H ₂ , N ₂ , O ₂ , CO, CO ₂ An overhead stream containing components such as and formaldehyde

The first distillation column, configured to separate a condenser, at least one condenser for condensing the overhead feed stream to form a condensed stream, and operatively connected to the condenser and separating the condensed stream into a vapor stream and a liquid stream. Having at least one separator suitable for

A hydrocarbon containing feed stream comprising an olefin monomer, optionally one or more comonomers and a hydrocarbon diluent,

  A bottoms stream comprising a hydrocarbon diluent substantially free of olefins,

  A substantially hydrogen free side stream comprising a hydrocarbon diluent and an olefin monomer, and

Olefin monomers, hydrocarbon diluents and formaldehyde, H ₂ , N ₂ , O ₂ , CO, CO ₂ An overhead stream containing components such as

And the second distillation column configured to separate the condensate into at least one condenser for condensing the overhead feed stream to form a condensed stream, and operatively connected to the condenser and separating the condensed stream into a vapor stream and a liquid stream. At least one separator suitable for the following, wherein some of the liquid stream is separated as a first side stream comprising a hydrocarbon diluent and an olefin monomer.

The invention will be further described in more detail below. The detailed description is given by way of example only and does not limit the invention. Reference numerals relate to the accompanying drawings.

1 shows a schematic diagram of an embodiment of a distillation system comprising two distillation columns according to the invention.
2 shows a schematic diagram of an embodiment of a distillation system comprising three distillation columns according to the invention.

The present invention relates to olefin monomers, one or more optional olefin comonomers, hydrocarbon diluents and H ₂ , N ₂ , O ₂ , CO, CO ₂ in other product streams. A process for separating a hydrocarbon-containing feed stream comprising a component such as and formaldehyde and preferably further comprises recycling the recovered product stream by separation in a polymerization process for preparing the bimodal polymer. The process is particularly optimized in terms of recycling the separated stream to and from the other product stream by controlling or redistributing the amount of product stream and the concentration of reactants recovered in the recovered stream.

The hydrocarbon-containing feed stream separated according to the invention will generally be an overhead stream from the purge tower and flash tank of the polymerization reactor, and the stream comprising solvent / diluent, polymer and unreacted monomer may be flashed or otherwise It is treated to remove diluents and monomers.

In another embodiment, the hydrocarbon containing feed stream may be an overhead stream from another distillation column.

The hydrocarbon-containing feed stream separated and recycled according to the present invention can be obtained from any polymerization process that produces an effluent comprising a slurry of particulate polymer solid suspended in a liquid medium comprising a diluent and an unreacted monomer. This reaction process is a process known in the art as particle formation polymerization, also called slurry polymerization.

As used herein, the term "polymeric slurry" or "polymer slurry" or "slurry" means a substantially two-phase composition comprising a polymer solid and a liquid. Solids include catalysts and polymerized olefins such as polyethylene. The liquid may contain an inert diluent such as isobutane with dissolved monomers such as ethylene, optionally comonomers such as 1-hexene, molecular weight regulators such as hydrogen, antistatic agents, antifouling agents, scavengers and other process additives. Include.

In a preferred embodiment, the invention relates to a process for separating the vapor stream exiting the effluent of the ethylene polymerization reaction. Suitable "ethylene polymerization" includes, but is not limited to, monopolymerization of ethylene and copolymerization of ethylene with higher 1-olefin comonomers such as butene, 1-pentene, 1-hexene, 1-octene or 1-decene. Currently preferred component streams separated in accordance with the invention comprise monomers such as ethylene, comonomers such as 1-hexene and diluents such as isobutane. However, it should be appreciated that the distillation system of the present invention is equally applicable to other monomer, comonomer and diluent systems as long as the feed vapor contains hydrocarbons that allow separation by distillation. Heavy components such as oligomers and formaldehyde, N ₂ , H ₂ Trace amounts of both light components such as and components such as O ₂ , CO and CO ₂ are generally also present in this effluent stream.

In particular, the present invention relates to a process for separating hydrocarbon-containing feeds, wherein the hydrocarbon-containing feed stream is used to prepare monomodal or bimodal polyolefins, such as monomodal or bimodal polyethylene (PE), and preferably bimodal polyethylene. Effluent stream obtained from the polymerization process for preparation. "Bimodal PE" refers to PE prepared using two reactors connected in series with one another, the operating conditions being different in the two reactors. "Monomodal PE" is produced in a single reactor or using two reactors in series with the same operating conditions.

As used herein, the term "separation" refers to the step of fractional distillation of a hydrocarbon containing feed stream into other fractions that can later be reused.

In addition, according to the process, the product stream separated from the hydrocarbon-containing feed stream is recycled in an olefin polymerization process, preferably an ethylene polymerization process, more preferably a polymerization process, in order to prepare a bimodal polyolefin, such as bimodal polyethylene.

As used herein, the term "bimodal polyolefin product" or "bimodal polyolefin" is intended to denote a polymer product comprising at least two fractions of the olefin polymer and one fraction having a lower molecular weight than the other fraction. As used herein, the term "bimodal polyethylene product" or "bimodal polyethylene" is intended to denote a polymer product comprising at least two fractions of ethylene polymer and one fraction having a lower molecular weight than the other fraction. Bimodal polyolefins, such as bimodal PE, can be produced in a sequential step process using different reactors in each reactor, using a polymerization reactor coupled in series, and the different fractions produced in different reactors each have their own molecular weight. Will have

In one embodiment, the polymerization process for preparing a bimodal polyolefin, such as bimodal polyethylene, is carried out in a double loop polymerization reactor unit consisting of two liquid full loop reactors, wherein the two liquid full loop reactors are operated from the first reactor. And first and second reactors connected in series by one or more settling legs of the first reactor connected to discharge the slurry to the second reactor. The first polyolefin fraction, diluent and catalyst can be transferred continuously or discontinuously from the first reactor to the second reactor.

In particular, in an embodiment, the first polyolefin, such as the first polyethylene fraction, is obtained in the presence of a catalyst by a first polymerization process of an olefin monomer such as ethylene in a diluent such as isobutane for example. This first polymerization process comprises feeding an olefin monomer, a diluent, at least one polymerization catalyst, optionally hydrogen and one or more optional olefin comonomer (s) such as 1-hexene to the first reactor and a first polyolefin Polymerizing the olefin monomer in a first reactor to produce a fraction, wherein the diluent and catalyst are transferred from the first reactor to the second reactor. In the second reactor, the second polyolefin fraction feeds into the second reactor an olefin monomer such as ethylene, for example a diluent such as isobutane, optionally hydrogen and one or more optional olefin comonomer (s) such as 1-hexene. and; Obtained by polymerizing the monomer and the at least one optional olefin comonomer (s) in the second reactor to produce a second polyolefin fraction in the second reactor. The second polyolefin fraction has a different molecular weight than the polyolefin fraction produced in the first reactor. The bimodal polyolefin product comprising the first and second polyolefin fractions is then recovered from the second reactor. This bimodal polyolefin product is then optionally combined with one or more additives and fed to the extruder.

In a particularly preferred embodiment of the above process, the second polyolefin fraction produced in the second reactor has a lower molecular weight than the first polyolefin fraction produced in the first reactor. In another preferred embodiment, hydrogen is added to the second reactor in which a second polyolefin fraction having a lower molecular weight than the first polyolefin fraction is produced.

In a preferred embodiment, the first polyethylene fraction prepared in the first reaction has, for example, a weight average molar mass of at least 300,000 g / mol, preferably from 300,000 to 700,000 g / mol and very particularly preferably from 300,000 to 600,000 g / mol. It is a high molecular weight (HMW) component composed of ethylene homopolymers or copolymers, preferably having a higher molecular weight than the second polyethylene fraction. In another preferred embodiment, the second polyethylene fraction prepared in the second reaction has a weight average molar mass of, for example, 8000 to 80,000 g / mol, preferably 20,000 to 70,000 g / mol and very particularly preferably 30,000 to 60,000 g / mol. It is composed of an ethylene homopolymer or ethylene copolymer having a low molecular weight (LMW) component, preferably having a lower molecular weight than the first polyethylene fraction.

The term "recycle" or "reuse" is used herein synonymously and both refer to a step of sending or feeding back a product stream separated from a hydrocarbon containing effluent stream to a polymerization reactor for use in the polymerization reactor.

Separation of the hydrocarbon containing feed stream, also referred to as the hydrocarbon containing effluent stream, into another separated product stream is carried out in a distillation system. The terms "distillation system" or "separation system", "recovery system" or "recycle compartment" are used as synonyms in some embodiments of the present invention and are all necessary equipment suitable for separating and recovering unreacted reactants from the effluent stream of the polymerization reaction. Says a system that includes. Such recovery systems generally include one or more distillation columns. The terms "distillation column", "separation tower" and "distillation column" may be used synonymously herein. In a preferred embodiment, the present distillation process is carried out in a distillation system comprising at least one distillation column, such as two or three distillation columns.

In a preferred embodiment, the at least one distillation column is a tray tower. Such tray tops include multiple trays of various designs that support liquid to provide better contact between vapor and liquid. The trays essentially operate as unit operations, with each tray achieving separation of one fraction between liquid and gas. It is clear that the greater the number of trays, the better the separation and the better the top performance. However, the use of multiple trays in a distillation column has significant disadvantages, particularly for the structure. Suitable distillation systems include distillation systems having a few trays, preferably less than 25, and even more preferably less than 20 tower (s). Nevertheless, although a distillation column with a few trays can be used in this process, as described in more detail below, the improved operation of the present distillation system allows to achieve a separation similar to that with a larger number of trays. . Advantageously, the application of this process has the advantages of less energy use and lower construction costs.

In an alternative embodiment, the at least one distillation column is a dividing wall distillation column. This tower is a distillation vessel having a vertical bulkhead separating one side from the other side with respect to a portion of the height of the vessel. Although such towers include a greater number of trays, the use of such a single tower may be advantageous for structural costs and energy requirements.

In a preferred embodiment, the at least one distillation column is a packing tower. Packing tower refers to a tower filled with inert solid particles.

The reboiler is used as a heat exchanger to provide heat to the bottom of the distillation column. The reboiler boils the liquid from the bottom of the distillation column to produce vapor that is returned to the tower to drive the distillation separation. The reboiler receives the liquid stream from the bottom of the tower and vaporizes the stream in part or in whole. Steam usually provides the heat needed for vaporization. According to the invention, part of the bottoms stream obtained in the distillation column is reboiled and the reboiled portion is returned to the distillation column.

According to the invention, separate streams of monomers, optionally comonomers and diluents are recycled for further use. The vapor feed stream to be separated, for example from the flash tank, also contains traces of both heavy components such as oligomers and lighter components including N ₂ , H ₂ , O ₂ , CO and CO _2. Light toxic ingredients such as and formaldehyde. Such components are also referred to herein as "toxic components" because such components are detrimental to the activity of the catalyst. Reintroduction of this into the polymerization reactor can greatly impede catalytic activity, thus reducing polymerization efficiency. Thus, having a recovery system suitable for the recovery stream of (co) monomers and diluents, with a suitable residual amount of such toxic components depending on the reuse conditions of the toxic components in the polymerization process, for example depending on the reactor in which the toxic components are fed to the bimodal system. Is the most important.

According to the invention, other diluent containing product streams can be separated from the feed stream and reused in the polymerization process to prepare the bimodal polymer. In particular, according to the invention, the hydrocarbon-containing feed stream is

I) a bottoms stream comprising a hydrocarbon diluent substantially free of olefins;

II) an overhead vapor stream comprising olefin monomers, hydrocarbon diluents and components such as formaldehyde, H ₂ , N ₂ , O ₂ , CO and CO ₂ ;

III) a first side stream comprising a hydrocarbon diluent and an olefin monomer; And

IV) separated into a second side stream substantially free of hydrogen and comprising a hydrocarbon diluent and an olefin monomer.

According to certain embodiments of the present invention, the hydrocarbon containing feed stream is condensed before being separated into the product stream defined above.

In another preferred embodiment, the hydrocarbon containing feed stream exits the overhead vapor stream from another (first) distillation column, the feed comprising: a1) a bottom stream comprising a hydrocarbon diluent and at least one optional comonomer, and a2) a hydrocarbon diluent And distillation conditions suitable to remove the overhead stream comprising the olefin monomer and components such as H ₂ , N ₂ , O ₂ , CO, CO ₂ and formaldehyde.

In particular, the overhead vapor stream obtained in step a2) is subjected to the following steps before condensation by the overhead condenser of the second distillation column:

The overhead stream exiting the first distillation column is condensed to form a condensate so that the formed condensate is stored in a reflux drum (first separator) of the first distillation column; The reflux drum is suitable for separating the vapor stream and the liquid stream;

The vapor stream is removed in the first separator,

The vapor stream is condensed to form a condensate and stored in a second separator suitable for separating the vapor stream and the liquid stream;

The liquid stream is removed in the second separator and the liquid stream is separated into a first side stream and the remaining streams;

The remaining stream is introduced into a second distillation column and subjected to distillation conditions.

In other words, in the reflux drum of the first distillation column (first separator), a portion of the stored condensate is removed as a liquid stream and fed to the first distillation column; The other part of the stored condensate is removed in the separator as a vapor stream. This vapor stream is composed of olefin monomers, hydrocarbon diluents and formaldehyde, H ₂ , N ₂ , O ₂ , CO and CO ₂ Contains ingredients such as The latter vapor stream is then condensed again by the overhead condenser of the second distillation column to form a condensate and then stored in the reflux drum of the second distillation column before being separated into the product stream defined above.

Bottom stream (I) comprises a hydrocarbon diluent substantially free of olefins. As used herein, the terms “substantially olefin free hydrocarbon diluent” or “olefin free diluent” and the like, include monomers of less than 5 ppm by weight and preferably less than 1 ppm by weight; It is used as a synonym for hydrocarbon diluent comprising an optional comonomer of less than 5000 ppm, preferably less than 1000 ppm and more preferably less than 100 ppm by weight. This bottoms stream is also substantially free of hydrogen and in particular contains only trace amounts of hydrogen, for example less than 10 ⁻² ppm, preferably less than 10 ⁻³ ppm. Substantially trace amounts of monomers such as ethylene and / or optional comonomers such as hexene and bottom streams of hydrocarbon diluents free of olefins such as isobutane from the distillation column free of lighter components such as hydrogen can be sent to the storage tank. And may be further used, for example, for flushing conduits and circulation pumps in polymerization reactors or for catalyst preparation, for example in mud pots. This olefin-free diluent can also be recycled to the polymerization stand, whether monopolymerized or copolymerized, anywhere in the process where pure diluent is required, such as catalytic dilution. When recycled in the bimodal polymerization process according to the invention, this bottoms stream is fed to the reactor where a polyolefin fraction having a higher molecular weight is prepared. According to this process, the amount of this bottoms stream can be reduced.

Formaldehyde, H ₂ , N ₂ , O ₂ , CO and CO ₂ Light components, such as, come out of the (second) distillation column with some residual monomer and diluent as overhead vapor stream (II). This overhead steam comes from the top of the distillation column. Preferably, the overhead stream is stored after condensation to form condensate. For example, this condensate is delivered to a separator, also referred to herein as a reflux drum or condensate vessel. A portion of this stored condensate is removed, for example it is removed from the separator as a vapor stream comprising aldehyde monomer and components such as formaldehyde, H ₂ , N ₂ , O ₂ , CO and CO ₂ ; When using ethylene monomers it is sent to a monomer recovery unit, for example an ethylene recovery unit (ERU). This light component is then further processed in a recovery unit, which further separates the light component from the remaining monomer and hydrocarbon diluent. Preferably, the amount of remaining monomers sent to the monomer recovery unit is less than 30%, preferably less than 20%, preferably less than 10%. Monomers and diluents recovered by the recovery unit are preferably reused in the polymerization process.

In an embodiment, under the conditions of the prior art, the stream conveyed to the ethylene recovery unit (ERU) comprises isobutane, ethylene, hydrogen, nitrogen and ethane. Ethylene and isobutane are further recovered from the ERU. Since the ethylene monomer is recovered in the additional side stream (IV) separated in the tower, the process of the invention can be used to reduce the amount of ethylene sent to the ERU. Preferably, the amount of remaining ethylene sent to the ERU is less than 30%, preferably less than 20%, preferably less than 10%.

The side stream (III) of hydrocarbon diluent leaving the distillation column is generally sent to a storage tank for further use. Preferably, the amount of additional components such as H ₂ , N ₂ , O ₂ , CO, CO ₂ and formaldehyde in the side stream is preferably lower than 500 ppm, for example contained in 50 to 500 ppm. In another preferred embodiment, the amount of monomer remaining in the side stream is lower than 10 wt%, for example comprised between 5 and 10 wt%. Large amounts of monomers in the storage tanks of the side stream product can lead to evaporation and substantially monomer losses. By keeping the amount of monomer in the side stream product below 10%, evaporation of the monomer from the storage tank can be reduced and storage of the side stream product at atmospheric conditions is possible.

The hydrocarbon diluent effluent as a side stream from the distillation column is, according to the invention, recycled in the polymerization process for preparing the bimodal polyolefin and used as a diluent, preferably it is a polymerization reactor, such as a first, in which a polyolefin fraction having a low molecular weight is prepared. It can be fed to two reactors.

In addition, the side stream (IV) of the hydrocarbon diluent exiting the distillation column is generally sent to a storage tank for further use. This second side stream is substantially hydrogen free and comprises a hydrocarbon diluent and an olefin monomer. As used herein, the terms "substantially hydrogen free" or "substantially hydrogen free hydrocarbon diluent" and the like refer to hydrocarbon diluents comprising less than 5 ppm by weight, preferably less than 1 ppm by weight and even more preferably less than 0.5 ppm by weight of hydrogen. Used as a synonym for. In another preferred embodiment, the amount of monomer remaining in the second side stream is lower than 5 wt%, for example 2-5 wt%.

The hydrocarbon diluent effluent as the second side stream from the distillation column is, according to the invention, recycled in the polymerization process for preparing the bimodal polyolefin and used as diluent, preferably it is a polymerization reactor in which a polyolefin fraction having a high molecular weight is prepared, For example, it may be fed to the first reactor.

In a preferred embodiment, a process is provided in which the second side stream is removed in the upper third of the second distillation column. Applicants show that removing the side stream in this portion of the tower will have the side stream with the most optimal composition for recycling in a reactor, such as a first reactor, in which a high molecular weight polyolefin fraction is prepared. In another embodiment, the process is performed in a distillation system that includes one or more tray distillation towers. In an embodiment, in the case of using a distillation column having 20 trays, the process is carried out in a second side stream in the tray of the distillation column selected from the upper second to seventh trays, preferably the upper third to sixth trays in the distillation column. To be removed. In this context "top" means counting from the top of the distillation column.

In one embodiment, the process is carried out in a distillation system comprising two distillation columns.

In another embodiment, the process is carried out in a distillation system comprising three distillation columns.

Referring now to the drawings, a recycling unit according to an embodiment of the present invention is schematically illustrated in FIG. 1. The recycle section shown consists of a monomer recovery unit represented by two distillation towers 1 and 2 and a box 19. The distillation column is preferably a tray top. The hydrocarbon containing feed stream 4 to be separated will generally be an overhead stream from the purge tower and flash tank of the polymerization reactor (not shown). The first distillation column 1 realizes a rough cut between a mixture of diluents such as isobutane, comonomers such as hexene and the weight coming out as the liquid bottom product 5. The heavy bottom product 5 can be further processed (not shown). The monomer remaining with some diluent and all light components exits the top of the first distillation column 1 as a vapor stream 6 for further separation. From the first distillation column 1 this overhead stream 6 is cooled in an overhead condenser 107. At the outlet of the condenser the stream 7 is collected in the reflux drum 108. The reflux drum 108 is suitable for separating the stream 7 into a liquid stream 8 and a vapor stream 106. The liquid stream 8 from the reflux drum is used as reflux to the first distillation column 1 and the vapor stream 106 obtained at the outlet of the reflux drum 108 is sent to the second distillation column. However, this vapor stream 106 is not thus fed directly to the second distillation column and it first condenses in the overhead condenser 207. Thus, the overhead condenser 207 of the second distillation column 2 receives the vapor stream 106 from the reflux drum 108 of the first distillation column 1 and also optionally overloads the second distillation column (described below). Receive head stream 12. Thus, overhead stream 12, described below, is combined with stream 106 for passage through condenser 207 and introduction into separator 208. At the outlet of the condenser 207 of the second distillation column, the stream 13 is preferably collected in a reflux drum 208 different from the reflux drum of the first distillation column described above. This reflux drum 208 is suitable for separating the liquid stream 15 and the vapor stream 14. The liquid stream is removed from the reflux drum 208 of the second distillation column 2 and thereafter comprises a first side stream 9 comprising a hydrocarbon diluent and an olefin monomer; And the remaining streams 16 are separated (separated). The remaining stream 16 is used as reflux to the second distillation column 2. In other words, monomers, diluents, formaldehyde, N ₂ , H ₂ Lighter components such as and O ₂ , CO and CO ₂ A portion of the liquid condensate 15 comprising a component such as is delivered from the condensate vessel 208 to the second distillation column 2 as a feed.

Thinner, H ₂ Lighter components and residual amounts of monomers such as are removed from the condensate vessel 208 as liquid side stream 9. This side stream 9 can be introduced into a storage container for storage and further manipulation. Preferably, this side stream comprises less than 10 wt% monomer and less than 500 ppm by weight of hydrogen. This first side stream 9 is usually recycled in the polymerization reactor. Preferably, this stream (9) is recycled in a polymerization process for preparing a bimodal polyolefin comprising at least two different polyolefin fractions obtained in two different polymerization reactors connected in series with one of said fractions. When having a molecular weight higher than the fraction, it is reused in the polymerization process in which the other polyolefin fraction is prepared. The vapor stream 14, separated from the reflux drum 208 of the second distillation column 2, recovered the monomers and H ₂ And N ₂ Light components, such as, are further cooled in a vent condenser (not shown) before being sent to the monomer recovery unit 19, which is sent to a flare.

Conditions inside the distillation column 2 can produce different product streams. Substantially pure diluent, the so-called "substantially olefin free" diluent, is obtained as liquid bottom product (11). This bottoms stream (11) comprising a diluent substantially free of olefin monomer is removed at the bottom of the distillation column (2). This bottom stream may pass through a water cooled heat exchanger (not shown) and may be introduced into a vessel (not shown) for storage and further manipulation. The second distillation column 2 further comprises a device for providing reboiling of the bottoms stream 11 under the control of the steam flow rate. For example, according to the invention, part of the bottoms stream 11 passes through the steam heating heat exchanger 18 and returns to the distillation column via line 17. The remaining diluent exits the tower 2 as a second liquid side stream 10 that is substantially free of hydrogen. According to a preferred embodiment, this side stream 10 is, for example, from the third, fourth, fifth or sixth top tray in the distillation column 2, through a line (not shown) for storage and further operation. It is removed from the upper third part of (2) and introduced into the container (not shown). Formaldehyde, H ₂ , N ₂ , O ₂ , CO and CO ₂ Light components, such as, come from distillation column 2 having olefin monomer and some residual diluent as vapor stream 12, which can be further condensed by condenser 207 according to another embodiment of the present invention. . The condensed vapor stream 13 then passes to separator 208.

The non-condensable vapor stream 14 is separated from separator 208 and passed through a vent condenser (not shown) to recover most of the entrained diluent, followed by further processing in olefin monomer recovery unit 19. .

Thus, the distillation process in the second distillation column is not only a diluent substantially free of olefins in the bottom stream (11) but also a residual amount of olefin monomers in the side stream (10) and a small amount, such as less than 5 ppm hydrogen and also a residual amount in the side stream (9). Allows separation of olefinic monomers and diluents containing slightly larger amounts of hydrogen. Both the diluent (11) and the diluent (10) substantially free of olefins can be recycled and reused in a polymerization process for preparing bimodal polyolefins, especially in reactors in which a high molecular weight polyolefin fraction is prepared. In addition, the diluent 9 can be recycled and reused in the polymerization process for preparing the bimodal polyolefin, especially in a reactor in which a polyolefin fraction having a low molecular weight is prepared. In a particularly preferred embodiment, the monomer recovery unit 19 can be omitted. Separation of side stream 10 comprising monomers and diluents dramatically reduces stream 14, leading to a competitive process in terms of monomer recovery without having to have a monomer recovery unit.

As shown in FIG. 2, the recirculation unit according to the embodiment of the present invention may consist of three distillation towers 1, 2, 3 in addition to the monomer recovery unit represented by the box 19. The hydrocarbon-containing feed stream (4) to be separated will generally be an overhead stream from the flash tank and purge tower of the polymerization reactor, the stream comprising solvents, polymers and unreacted monomers in order to remove solvents or diluents and monomers from the stream. Flashed or otherwise processed. The first distillation column 1 realizes a rough cut between the mixture of the diluent, comonomer and heavy product coming out as the liquid bottom product 5. The heavy bottom product is further processed in distillation column 3 and separated into three product streams: the diluent vapor coming out of the top product 22 is first cooled in the overhead condenser 307 of the third distillation column. The stream 23 is then collected in the reflux drum 308 of the third distillation column 3 at the outlet of this condenser 307. This reflux drum 308 is suitable for separating and collecting the sufficiently condensed stream 23. This liquid then exits the reflux drum 308 as a liquid stream 24. The liquid stream 24 can be further divided into a first liquid stream 26 which is sent to the third distillation column as reflux and a second liquid stream 25 which can be recycled to the first distillation column.

The purified liquid comonomer stream 21 is withdrawn from the tray just above the top sump and sent to the reservoir for recycling to the polymerization reactor (s). Heavy components 20 are recovered from the tower sump as the drainage procedure commences at the high bottom temperature of the tower.

The remaining monomers and diluents, together with all the light components from the top 6 of the first distillation column 1, are sent to the distillation column 2 as a vapor stream for further separation according to the process as described for FIG. Lose. The stream will condense and separate at least twice in the condensation / separation cycle before entering the second distillation column 2 and being treated in the same manner as described for FIG. 1. Distillation column 2 is used to generate four product streams: A substantially pure diluent, a so-called "substantially olefin free" diluent, is obtained as liquid bottom product 11. Light components, such as formaldehyde, H ₂ , N ₂ , O ₂ , CO and CO ₂ , come out of the distillation column (2) with the olefin monomer and some residual diluent as vapor stream (12), which is an embodiment of the present invention. Thus further purified in the monomer recovery unit shown in box 19 and further condensed before being separated off. The remaining diluent exits the tower 2 as liquid side stream 10. In addition, a separate side stream of diluent and monomer (9) is also recycled and reused in the polymerization process.

In addition, while the invention is illustrated by the following examples of preferred embodiments of the invention, it will be understood that this example is included for purposes of illustration only and does not limit the scope of the invention unless otherwise indicated.

Example

This example shows a hydrocarbon-containing feed stream according to the process of the present invention, a) a first side stream comprising isobutane and ethylene, b) a second side stream substantially free of hydrogen and comprising isobutane and ethylene, c A) a bottoms stream comprising isobutane substantially free of ethylene and d) an overhead vapor stream comprising components such as isobutane, ethylene and formaldehyde, H ₂ , N ₂ , O ₂ , CO and CO ₂ Explain what to do. A recycling compartment according to an embodiment of the invention in which this process is performed is shown in FIG. 1. This recycle compartment setup can be used to recover many or most of isobutane while minimizing ethylene loss.

In this embodiment, the second side stream is withdrawn from the sixth tray (counted from the top) of the second tower. In this case, 800 kg / hr reboiler steam consumption is required and consequently the total flow rate to the ERU is calculated to be about 325 kg / hr. This calculated value will be compared to the conditions applied in the recycling system where the second side stream is not separated, which means that line 10 is absent and this flow rate is added to the flow rate exiting the tower through line 11. In this latter case, the steam flow rate reaches 1500 kg / hr and the flow rate to the ERU exceeds 700 kg / hr.

This value demonstrates that separating the second side stream that is substantially hydrogen free can advantageously greatly reduce the basic requirement for isobutane (bottom stream) free of ethylene. This makes it possible to reduce steam consumption even in excess of 700 kg / hr in the (second) distillation column. In addition, this second side stream will absorb some ethylene and will greatly reduce, preferably greater than 50%, an uncondensable vapor stream that still contains hydrogen removed from the separator of the second distillation column. The loss of ethylene will be substantially reduced.

Table 1 given below compares the composition of the second side stream 10 (FIG. 1) separated in accordance with the present process when compared to a conventional side stream exiting a conventional recycle system.

Side stream according to the present invention Conventional side stream Hydrogen (ppm) 0.33 318.54 Ethylene (% wt) 2.83 7.28 Isobutane (% wt) 97.16 92.65 Hexene (ppm) 0.02 0.02

As shown in Table 1, having an additional first side stream 9 allows the separation of the second side stream 10 from the top of a distillation column comprising isobutane and ethylene but substantially free of hydrogen. For comparison, in a conventional system, the side stream separated from the distillation column contains approximately similar amounts of isobutane and ethylene but much more hydrogen.

Claims (14)

Process for recycling a product stream separated from a hydrocarbon containing feed stream comprising an olefin monomer, at least one optional olefin comonomer, a hydrocarbon diluent and a component comprising H ₂ , N ₂ , O ₂ , CO, CO ₂ and formaldehyde Wherein the hydrocarbon-containing feed stream is
a) the feed stream is
a1) bottom stream (5) comprising a hydrocarbon diluent and at least one optional comonomer, and
a2) overhead stream comprising a hydrocarbon diluent, an olefin monomer and a component comprising H ₂ , N ₂ , O ₂ , CO, CO ₂ and formaldehyde (6)
Introducing the feed stream into a first distillation column (1) to undergo distillation conditions to remove the;
b) in a separator 108 for condensing the overhead stream 6 exiting the first distillation column 1 in step a2) to form a condensate and separating the vapor stream 106 and the liquid stream 8. Storing the condensate;
c) removing from the olefin monomer, hydrocarbon diluent and formaldehyde, H _2, N _2, O _2, the vapor stream 106, the separator (108 containing components that include CO and CO _2);
d) storing the condensate in a separator 208 for condensing the vapor stream 106 removed in step c) to form a condensate 13 and separating the vapor stream 14 and the liquid stream 15. step;
e) removing the liquid stream (15) of step d) from the separator (208);
f) separating the liquid stream (15) into a first side stream (9) comprising a hydrocarbon diluent and an olefin monomer and the remaining stream (16);
g) the remaining stream (16) is introduced into a second distillation column (2), and the remaining stream (16) is
g1) bottom stream (11) comprising hydrocarbon diluent free of olefins,
g2) a hydrogen free second side stream 10 comprising a hydrocarbon diluent and an olefin monomer, and
g3) an overhead vapor stream (12) comprising an olefin monomer, a hydrocarbon diluent and a component comprising formaldehyde, H ₂ , N ₂ , O ₂ , CO and CO ₂
Separated by the step of undergoing distillation conditions to remove
The first side stream 9 and the second side stream 10 are also recycled in a polymerization process to prepare a bimodal polyolefin comprising at least two different polyolefin fractions obtained in two different polymerization reactors connected in series with each other. One of the fractions has a higher molecular weight than the other fraction, the second side stream 10 is reused in a polymerization process in which a polyolefin fraction having a higher molecular weight is prepared, and the first side stream 9 ) Is a process for recycling a product stream separated from a hydrocarbon containing feed stream which is reused in a polymerization process in which the other polyolefin fraction is prepared. The method of claim 1,
h) condensation of the overhead vapor stream 12 obtained in step g3) in the mixture of vapor stream 106 removed in step c) to selectively form condensate, and the condensate thus formed in separator 208 Storing the; And
i) subjecting the stored condensate obtained in step h) to steps e) to g), wherein the product stream separated from the hydrocarbon containing feed stream is recycled. 3. The method according to claim 1 or 2,
and wherein said second side stream (10) of step g2) comprises at least 2 wt% of olefinic monomers. 3. The method according to claim 1 or 2,
and wherein said second side stream (10) of step g2) comprises up to 5 ppm by weight of hydrogen. 3. The method according to claim 1 or 2,
and wherein said first side stream (9) of step f) comprises less than 10 wt% olefin monomer. 3. The method according to claim 1 or 2,
The first side stream (9) of step f) comprises less than 500 ppm by weight of hydrogen, wherein the product stream separated from the hydrocarbon containing feed stream is recycled. 3. The method according to claim 1 or 2,
The bottom stream (11) of step g1) comprises less than 5 ppm of olefin monomer and optionally less than 5000 ppm of olefin comonomer. 3. The method according to claim 1 or 2,
and the second side stream (g) of step g2) is removed in the upper third of the second distillation column. 3. The method according to claim 1 or 2,
The bottom stream 11 of step g1) is reused in a polymerization process for preparing a bimodal polyolefin comprising at least two different polyolefin fractions obtained in two different polymerization reactors connected in series with one of said fractions. A process for recycling a product stream separated from a hydrocarbon containing feed stream, having a higher molecular weight than the other fraction, wherein the bottom stream (11) is reused in a polymerization process in which a polyolefin fraction having a higher molecular weight is prepared. 3. The method according to claim 1 or 2,
Removed from the condensate stored in step d) a vapor stream (14) comprising an olefin monomer and a component comprising formaldehyde, H ₂ , N ₂ , O ₂ , CO and CO ₂ , said vapor stream (14) Recovering the olefin monomer from the hydrocarbon product feed stream. 3. The method according to claim 1 or 2,
1) a side stream 21 comprising one or more optional comonomers,
2) an overhead stream 22 comprising a hydrocarbon diluent and optionally a comonomer, and
3) bottom stream containing heavy components (20)
Introducing a bottoms stream of step a1) into a third distillation column (3) such that the bottoms stream (5) is subjected to distillation conditions to remove the product stream separated from the hydrocarbon-containing feed stream. Way. 3. The method according to claim 1 or 2,
The hydrocarbon containing feed stream (4) comprising an olefin monomer, at least one optional olefin comonomer and a hydrocarbon diluent is a product separated from the hydrocarbon containing feed stream, which is an effluent stream obtained in the polymerization process for preparing monomodal or bimodal polyolefins. Method for recycling the stream. A polymerization apparatus for preparing a bimodal polyolefin comprising two different polymerization reactors operatively interconnected in series to a distillation system,
The distillation system comprises a first distillation column (1) and a second distillation column (2) operably interconnected in series,
A hydrocarbon-containing feed stream (4) comprising an olefin monomer, optionally one or more comonomers and a hydrocarbon diluent,
Bottom stream (5) comprising a hydrocarbon diluent and at least one optional comonomer, and
Said first distillation column 1 configured to separate into an overhead stream 6 comprising a hydrocarbon diluent, an olefin monomer and a component comprising H ₂ , N ₂ , O ₂ , CO, CO ₂ and formaldehyde,
At least one condenser 107 for condensing the overhead feed stream 6 to form a condensed stream 7 and a condensed stream 7 operably connected to the condenser stream 7. ) And at least one separator 108 for separating into a liquid stream 8,
A hydrocarbon-containing feed stream 106 comprising an olefin monomer, optionally one or more comonomers and a hydrocarbon diluent,
Bottom stream (11) comprising hydrocarbon diluent free of olefins,
A hydrogen free side stream (10) comprising a hydrocarbon diluent and an olefin monomer, and
Said second distillation column (2) configured to separate into an overhead stream (12) comprising an olefin monomer, a hydrocarbon diluent and a component comprising formaldehyde, H ₂ , N ₂ , O ₂ , CO, CO ₂ ,
Vaporize the condensed stream 13 and at least one condenser 207 for condensing the overhead feed stream 12 to form a condensed stream 13 and operably connected to the condenser 207. At least one separator 208 for separating into a stream 14 and a liquid stream 15, wherein a portion of the liquid stream is separated as a first side stream 9 comprising a hydrocarbon diluent and an olefin monomer to polymerize. Polymerization apparatus recycled in the reactor. Feeding an olefin monomer, diluent, at least one polymerization catalyst, optionally hydrogen and one or more optional olefin comonomer (s) to the first reactor,
Polymerizing the olefin monomer in the first reactor to produce a polymer slurry comprising a first polyolefin fraction in a diluent,
Moving said polymer slurry from said first reactor to a second reactor,
Feeding an olefin monomer, diluent, optionally hydrogen and one or more optional olefin comonomer (s) to the second reactor,
Polymerizing the olefin monomer and the at least one optional olefin comonomer (s) in the second reactor to produce a slurry in a diluent comprising a second polyolefin fraction having a molecular weight different from the polyolefin fraction produced in the first reactor. step,
Evacuating from the second reactor a slurry comprising bimodal polyolefin in the diluent,
Recovering the bimodal polyolefin from the slurry by separating at least most of the diluent from the slurry in a hydrocarbon containing feed stream, and
Subjecting the hydrocarbon-containing feed stream to a process according to claim 1 or 2,
The process of claim 1 or 2 in a polymerization process for preparing a bimodal polyolefin having at least two different polyolefin fractions obtained in two different polymerization reactors interconnected in series, one of which fractions having a higher molecular weight. How to use the method according to.

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